Shock absorbing devices are used in a wide variety of vehicle suspension systems for controlling motion of the vehicle and its tires with respect to the ground and for reducing transmission of transient forces from the ground to the vehicle. Shock absorbing struts are a common component in most aircraft landing gear assemblies. The shock struts used in the landing gear of aircraft generally are subject to more demanding performance requirements than most, if not all, ground vehicle shock absorbers. In particular, shock struts control motion of the landing gear, and absorb and damp loads imposed on the gear during landing, taxiing and takeoff.
A shock strut generally accomplishes these functions by compressing a fluid within a scaled chamber formed by hollow, telescoping cylinders. Typically, at least two bearing assemblies provide for sliding engagement of the telescoping cylinders. The fluid generally includes both a gas and a liquid, such as hydraulic fluid or oil. One type of shock strut generally utilizes an “air-over-oil” arrangement, wherein a trapped volume of gas is compressed as the shock strut is axially compressed, and a volume of oil is metered through an orifice. The gas acts as an energy storage device (e.g., like a spring), so that upon termination of a compressing force, the shock strut returns to its original length. Shock struts also dissipate energy by passing the oil through the orifice so that as the shock absorber is compressed or extended, its rate of motion is limited by the damping action from the interaction of the orifice and the oil.